# STRAIN AND CURVATURE AS FACTORS FOR PREDICTING PAVEMENT FATIGUE

The fatigue cracking of asphalt pavements is caused by the repeated applications of excessive tensile strains in the asphalt-bound layer. To predict fatigue, it is necessary to determine the maximum tensile strain at the bottom of the asphalt-bound layers. Two methods are suggested for determining the maximum tensile strain, based on the two-layer elastic theory. The use of two-layer theory, instead of the conventional three- or multiple-layer theory, is based on the fact that the tensile strains at the bottom of the asphalt-bound layer depend on the property of the asphalt-bound layer relative to that of the underlying layers. Any multi-layer systems can thus be reduced to a system, if an average modulus of elasticity is used to represent the combined effect of all the underlying layers. Fortunately, the moduli of untreated granular materials and soils generally fall within narrow ranges, and typical values can usually be assumed. To facilitate the application of the two methods, simple charts are presented for determining the maximum tensile strain under a set of dual tires. The first method, which can be used for pavement deisgn, requires a knowledge of the elastic moduli of both layers and the thickness of the ashpalt-bound layer. By entering these variables into the chart, the maximum tensile strain can be easily determined. The second method, which can be used for pavement evaluation, requires the measurement of curvature on the pavement surface. Knowing the curvature, the modulus ratio, and the thickness of the asphalt-bound layer, the maximum tensile strain can be determined from the charts. It was found that for asphalt-bound layers of 4 in. thick or more the curvature-tensile strain ratio is practically independent of the modulus ratio. By simply measuring the curvature on the surface, the maximum tensile strain can be estimated, and the adequacy of the pavement to withstand fatigue evaluated. Examples are given to illustrate the use of these charts for pavement design and evaluation. /Author/

• Supplemental Notes:
• Presented at the Third International Conference on the Structural Design of Asphalt Pavements, Grosvenor House, Park Lane, London, England, Sept. 11-15, 1972.
• Corporate Authors:

International Conf Struct Design Asph Pvmts (3rd)

University of Michigan, Department of Civil Engineering
Ann Arbor, MI  United States  48104

International Conf Struct Design Asph Pvmts (3rd)

University of Michigan, Department of Divil Engineering
Ann Arbor, MI  United States  48104

Interrational Conf Struct Design Asph Pvmts (3rd)

University of Michigan, Department of Civil Engineering
Ann Arbor, MI  United States  48104
• Authors:
• Huang, Y H
• Conference:
• Publication Date: 1972-9

## Media Info

• Features: Figures; References;
• Pagination: p. 622-628
• Serial:
• Volume: 1

## Filing Info

• Accession Number: 00261931
• Record Type: Publication
• Report/Paper Numbers: Proceeding
• Files: TRIS
• Created Date: Oct 22 1974 12:00AM